In previous studies with human and infra-human infants we found that vestibular-proprioceptive stimulation had highly significant effects on the behavior and development of neonates. With such stimulation, human infants we soothed and responded with visual alertness and attentiveness and rat pups showed more exploratory behavior and greater weight gain. We are now proposing an intervention study with prematures in which we will provide patterned vestibular- proprioceptive stimulation with the aim of furthering the neurological and behavioral maturation of these infants at risk. Clinical and developmental assessments will be made longitudinally during the entire hospital stay which will compare the progress of two experimental groups and a control group. We will continue our studies of infant motility and crying patterns. With the help of a specially designed activity monitor which provides counts of crying and non-crying motions of various amplitudes, the distribution of rest-activity cycles, and the cumulative time the infant is crying and attended by a caretaker, we will monitor the motility and crying patterns of normal, full-term neonates, of special groups of infants at risk, and of prematures from 28 weeks gestational age onward. By studying the ontogeny of motility and crying patterns in a large group of infants, we hope to establish some developmental norms for the frequency, amplitude, and distribution of motions which may typify a given gestational age.